Fuel cell system

ABSTRACT

The invention relates to a fuel cell system ( 11, 111 ) comprising an anode chamber ( 13, 113 ) and a cathode chamber ( 14, 114 ) which are separated from each other by a proton conducting membrane ( 15, 115 ). When the fuel cell system is operated, fuel, in particular H 2  or a water/methanol mixture, can be fed to the anode chamber and an oxidant, in particular oxygen, can be fed to the cathode chamber. In standby mode, the cathode chamber ( 14, 114 ) does not allow flow through and the oxidant and fuel are present in both the cathode chamber ( 14, 114 ) and the anode chamber ( 13, 113 ), respectively. The fuel cell system remains at operating temperature in the standby mode. This enables the fuel cell system ( 11 ) to be used as a combined interruption-free power supply unit and backup unit.

BACKGROUND OF THE INVENTION

The invention concerns a fuel cell system as well as a method foroperation of a fuel cell system, having an anode chamber and a cathodechamber which are separated from each other by a proton conductingmembrane, wherein, during an operational state, a fuel can be introducedto the anode chamber and an oxidant, in particular oxygen, can beintroduced to the cathode chamber. The invention also concerns a systemfor interruption-free power supply to at least one electrical user whoseenergy is normally extracted from an alternating current power networkand, in the event of failure of the alternating current power network,energy can be extracted from a fuel supply system. The invention alsoconcerns a method for operating the system.

German patent application P 195 38 381 describes a system forinterruption-free power supply to electrical users with which, in theevent of power mains failure, a so-called PEM fuel cell (polymerelectrolyte membrane) takes over power supply to the user. Towards thisend, inlets introduce fuel and an oxidant to the fuel cell. Valves aredisposed in these inlets which are closed in the standby state of thefuel cell when the alternating current power network is functioning.During the standby state of the fuel cell, no fuel and no oxidant gainsentrance into the fuel cell. Should the power network fail, the valvesare opened and the fuel and oxidant are introduced into the fuel cell.The fuel cell is then transferred into an operational mode. In thisoperational mode, the fuel and the oxidant react in the fuel cell toproduce electrical energy.

The transition from the standby state into the operational state of thefuel cell is therefore effected with the assistance of valves. Thesetypes of valves, in particular electromagnetically operated valves, havea response time of at least approximately 100 ms. Power network failurecan therefore only be compensated for following an interruption time ofapproximately 100 ms.

It is the underlying purpose of the invention to create a fuel cellsystem as well as a method for operation of a fuel cell system and asystem for interruption-free power supply with which a downtime of lessthan 100 ms can be achieved.

SUMMARY OF THE INVENTION

This purpose is achieved in accordance with the invention with a fuelcell system or a method of the above mentioned kind in that, in thestandby state, the oxidant is present in but does not flow through thecathode chamber. The oxidant thereby preferentially exercises pressureon the membrane.

The oxidant is therefore also present in the cathode chamber in thestandby state when the alternating current power network is functioning.When the power network breaks down it is therefore not necessary, as wasthe case in prior art, to first open a valve in order to introduce theoxidant into the cathode chamber. Rather, the oxidant is already presentin the cathode chamber and the fuel cell system can therefore take overcurrent supply to the user without delay.

The invention therefore facilitates downtimes between the breakdown ofthe alternating current power network system and takeover by the fuelcell system which are substantially less than 100 ms. The fuel cellsystem in accordance with the invention can therefore preferentially beused in a system for interruption-free power supply to electrical users.

In a preferred embodiment of the invention, the cathode chamber isconnected to a cathode outlet having a blocking member, in particular amagnetic valve, which is closed in the standby state. In this manner,the cathode chamber can be closed in the standby state at least one sideso that the oxidant is present in but cannot flow through the cathodechamber. In the operational state, the blocking member is opened so thatthe oxidant can then flow through the cathode chamber. Continuousreactions between the fuel and the oxidant then occur.

In a preferred embodiment of the invention, the cathode chamber isconnected to a first cathode inlet which is connected to at least onetank, filled with oxidant or the like, via a blocking member, inparticular a magnetic valve and/or a pressure reducer. This represents aparticularly simple and economical method for making the oxidantavailable during the standby state.

In an additional advantageous embodiment of the invention, the cathodechamber is connected to a second cathode inlet which is connected, via ablocking member and preferentially a magnetic valve, to a compressor orthe like which intakes a gas, preferentially air. The oxidant, inparticular oxygen, must not thereby be extracted from the tank duringthe operational state, rather can easily e.g. be extracted from the air.The oxidant is therefore initially taken from the tank and introducedinto the cathode chamber and Subsequent thereto, for prolongedoperation, a gas, in particular air, is suctioned into the cathodechamber. The oxidant contained in the tank is therefore not used-upduring the operational state of the fuel cell system so that a fillingup or an exchange of the tank is only rarely required.

In a particularly preferred embodiment of the invention, the fuel ispresent in the anode chamber during the standby state. The fuelpreferentially exercises pressure on the membrane. Towards this end, itis possible for the fuel to either be statically disposed in the anodechamber, e.g. in the form of hydrogen from a pressure vessel, or thefuel, e.g. a liquid fuel can flow in intervals or continuously throughthe anode chamber. It is only important that the fuel be present in theanode chamber at the membrane. Therefore, the fuel is also present inthe anode chamber during the standby state when the alternating currentpower network is functioning. When the power network breaks down, it isnot necessary, as was the case in prior art, to initially open a valveto introduce the fuel into the anode chamber. Rather, the fuel isalready present in the anode chamber and the fuel cell system cantherefore take over current supply to the user without any delay.

In a particularly preferred embodiment, the fuel cell is maintained atan optimal operating temperature in the standby state. The powercapability of the fuel cell at 80 to 100° C. is approximately twice thatat room temperature (20 to 30° C.). This can be effected by temperaturecontrolling a circuit having liquid fuel or with a separate temperaturecontrolled circuit. Heating is effected by the power mains. This measureimproves the instantaneous efficiency of current delivery in the eventof network failure. In this manner, the number of cells (stack) can besubstantially reduced, which is definitive for investment costs.

The method in accordance with the invention therefore introduces a fuelcell system which, in the standby state with functioning alternatingcurrent power network, has a cathode chamber closed at at least oneside, but filled with an oxidant so that the oxidant is present in thecathode chamber. The anode chamber is filled with fuel. As a result, thefuel cell system in accordance with the invention produces an off-loadvoltage in the standby state.

Since the cathode chamber has no through flow in this state, the fuelcell system can only deliver current for a short period of time whenloaded, e.g. after a power network failure. One overcomes this situationby opening the blocking member of the cathode chamber during thetransition from the standby state into the operational state. Thecathode chamber is thereby no longer closed-off and the oxidant can flowthrough the cathode chamber. In this manner, continuous electrochemicalreactions can occur in the fuel cell so that current can be continuouslyproduced. In this operational state, the fuel cell system can thenreplace the broken down alternating current power network. An H₂/O₂ cellof approximately 1500 l delivers a power of 250 kW at 80° C. over aperiod of several hours with low (less than 2 bar) sound levels andsubstantially without pollutant emission.

The amount of time required to open the blocking member assumes valuesof approximately 100 ms for electromagnetically operated valves. Thisresponse time of approximately 100 ms does not however present a problemto the invention, since sufficient reactions can already occur duringthis time. In prior art, the system did not allow reactions during thetime when the valve was being opened. The system in accordance with theinvention delivers current within 10 ms.

By exercising pressures in the cathode chamber and the anode chamberwhich are preferentially of equal size and e.g. assume values ofapproximately 2 bar, no pressure difference is present across themembrane so that no damage to the membrane can occur.

In an advantageous improvement of the invention, the anode chamber isconnected to an anode circuit for introduction of a liquid fuel (e.g.methanol). It is particularly advantageous when this anode circuitcomprises a pump and a heater. The fuel can thereby be caused to flowthrough the anode chamber in a particularly simple manner. In addition,the fuel cell can be easily maintained in the standby state at a desiredtemperature.

In an advantageous embodiment of the invention, the anode circuit ispressurized. The fuel thereby exercises a permanent pressure on themembrane. This improves the reactions between the fuel and the oxidantsuch that the fuel cell system in accordance with the invention canswitch from the standby state into the operating state in a particularlyrapid fashion. In addition, the pressure exercised by methanol fuel inthe anode circuit substantially reduces losses due to carbon dioxidedischarge.

In an advantageous improvement of the invention, the anode chamber andcathode chamber are accommodated in a gas-tight and optionallyadditionally heat-insulated housing. In this manner, one prevents thetemperature of the fuel in the anode circuit from being substantiallyinfluenced by external factors and is therefore reduced to only aninsignificant extent, in particular during the standby state. It isparticularly advantageous when the housing is pressurized, in particularsubjected to nitrogen pressure. This substantially suppresses leakagefrom the anode chamber and/or the cathode chamber. In addition, thenitrogen pressure prevents boiling of a liquid fuel in the anodecircuit, in particular boiling of a methanol/water mixture.

Further features, applications, and advantages of the invention can bederived from the following description of the invention usingembodiments represented in the figures. All features shown and describedconstitute aspects of the invention either alone or in arbitrary mutualcombination independent of their composition in the patent claims ortheir dependencies as well as independent of their formulation orrepresentation in the description or in the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic block circuit diagram of an embodiment of asystem in accordance with the invention for interruption-free powersupply to at least one electrical user;

FIG. 2 shows a schematic block circuit diagram of an embodiment of afuel cell in accordance with the invention for use in the systemaccording to FIG. 1;

FIG. 3 shows a schematic block circuit diagram of a second embodiment ofa fuel cell in accordance with the invention for use in a systemaccording to FIG. 1;

FIG. 4 shows a schematic block circuit diagram of the gas inlet to thefuel cell shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a system 1 for interruption-free power supply to at leastone electrical user. A system of this kind can e.g. be used as aso-called interruption-free current supply (ICS) for a computer centeror the like. The user, e.g. an electrical unit in the computer center,is normally connected to an alternating current power network. Shouldthe network break down, the system 1 takes over current supply to theuser. One normally requires that the system 1 be capable of taking overthe power supply within several milliseconds.

FIG. 1 shows a plurality of electrical users 2, represented byresistance symbols. The users 2 are connected to a rapidly switchingswitch 4 via a common bypass switch 3. The bypass switch 3 can beoperated by hand. Switch 4 can be a contact-free switching element, e.g.anti-parallel circuited thyristors or the like.

The input to circuit 4 is connected to an alternating current powernetwork 6 via a choke 5. In addition, a first and optionally anadditional DC-AC converter 7 are circuited in parallel with respect toeach other and are connected to the output side of the switch 4proximate the user.

An auxiliary rectifier 8 is circuited between the alternating currentpower network 6 and the DC-AC converter 7 which covers the no-loadlosses of the DC-AC converter 7. In addition, the auxiliary rectifier 8feeds a control unit 9 which is connected to the control input of theswitch 4.

The input rectifiers of the DC-AC converter 7 are connected to acapacitor 10, circuited to ground, and to a fuel cell system 11 via anelectrical cable 12.

During normal operation of the alternating current power network 6,current flows via the closed switches 4 and 3 to the users 2. A failurein the alternating current power network 6 is recognized by the controlunit 9. The control unit 9 then switches the switch 4 into its openstate. The current supply to the user 2 is then taken over by the fuelcell system 11 via the DC-AC converter 7. The capacitor 10 therebyserves to bridge switching from the alternating current power network 6to the fuel cell system 11 and also smoothes out the voltage produced bythe fuel cell system 11.

A first embodiment of the fuel cell system 11 is shown in detail in FIG.2. It has an anode chamber 13 and a cathode chamber 14 which areseparated from each other by means of a proton conducting membrane 15.The anode chamber 13, the cathode chamber 14 and the membrane 15 form aso-called direct methanol fuel cell (DMFC) in which electrical energy isproduced by electrochemical processes. This energy, in the form ofelectrical voltage and current, can be tapped via the electrical cable12.

The anode chamber 13 is connected to an anode circuit 16 which,departing from an anode outlet 17, via a cooler 18, a two chamberseparator 19, a heater 20, a thermostat valve 21 and a cooling pump 22,is connected to an anode inlet 23. An additional separator 24 isconnected to both the anode outlet 17 as well as to the thermostat valve21. A tank 26 is connected to the anode circuit 16 upstream of thecooling pump 22 via a dosing pump 25.

The cathode chamber 14 is connected, via a cathode outlet 27, to amagnetic valve 28 whose output is connected to a catalytic burner 29. Inaddition, the cathode chamber 14 is connected to a tank 33 via a cathodeinlet 30, a pressure reducer 31, and a magnetic valve 32. The cathodeinlet 30 is likewise connected to a magnetic valve 34 which, via abypass magnetic valve 35, is connected to that side of the catalyticburner 29 opposite the magnetic valve 28.

The two sides of the bypass magnetic valve 35 are connected to theoutputs of a compressor-expander unit 37, driven by a motor 36. One ofthe inputs of the unit 37 intakes air via filter 38. The other input ofthe unit 37 is connected, via a cooler 39, a drain 40, and a pump 41 tothe separator 19 of the anode circuit 16. This separator 19 is alsoconnected to the catalytic burner 29 via a magnetic valve 42.

The anode chamber 13, the cathode chamber 14, the membrane 15, the anodecircuit 16 having the anode outlet 17, the cooler 18, the separator 19,the heater 20, the thermostat valve 21, the coolant pump 22, the anodeinlet 23 and the separator 24, as well as the cathode outlet 27, themagnetic valve 28, the cathode inlet 30 and the magnetic valve 34 areaccommodated in a housing 43. The housing 43 is gas-tight, pressureresistant and heat insulated. The housing 43 is connected to a tank 45via a pressure reducer 44. The tank 45 is also connected to theseparator 19 of the anode circuit 16 via the pressure reducer 44.

Oxygen is present in tank 33, which is provided as the oxidant. Tank 26contains methanol, which is provided as the fuel. Nitrogen is present intank 45, which is provided as a pressure agent. In addition, the anodecircuit 16 contains cooling water.

When the alternating current power network 6 functions, the fuel cellsystem 11 is in a standby state in which the magnetic valve 28 isclosed. The magnetic valves 34 and 42 as well as the bypass valve 35 arealso closed. The magnetic valve 32 is opened.

The closed magnetic valves 28 and 34 and the opened magnetic valve 32cause the cathode chamber 14 to be filled with oxygen from the tank 33.The oxygen is then present in the cathode chamber 14 and exerts pressureon the membrane 15. This pressure can be adjusted to a desired value viathe pressure reducer 31, e.g. to 2 bar. However, oxygen cannot flowthrough the cathode chamber 14 due to the closed magnetic valve 28.

A methanol/water mixture is present in the anode chamber 13 and in theanode circuit 16. The temperature of the methanol/water mixture assumesvalues of approximately 110°. The coolant pump 22 and the dosing pump 25as well as the pump 41 are switched-off. The heater 20 and thecompressor-expander unit 37 are likewise switched-off.

Should the temperature of the methanol/water mixture fall-off over timeto a temperature of e.g. approximately 100°, the heater 20 and thecoolant pump 22 are switched-on. The methanol/water mixture is therebycirculated through the anode circuit 16 and warmed.

The electrical components of the fuel cell system 11 which are switchedon during the standby state are provided with electrical energy from thealternating current power network 6.

The nitrogen pressure in the tank 45 is transferred into the anodechamber 13 via the separator 19 of the anode circuit 16. This pressurecan thereby be adjusted by means of the pressure reducer 44 to a desiredvalue, e.g. 2 bar. The methanol/water mixture is thereby present on themembrane 15 at this pressure.

The membrane 15 is proton conducting. The methanol/water mixture presentin the anode chamber 13 is converted into carbon dioxide with therelease of hydrogen protons and electrons. The hydrogen protons passthrough the membrane 15 and react with the oxygen in the cathode chamber14 to produce water. The electrons produced by these chemical reactionscreate the electrical current and voltage at the electrical cable 12.

In the standby state of the fuel cell system 11, the cathode chamber 14is closed off at at least one side so that oxygen is present in, butcannot flow through the cathode chamber 14. Consequently, the abovementioned chemical reactions occur until the oxygen supply is exhausted.This generates an electrical voltage on the cable 12.

A second embodiment of the fuel cell system is shown in detail in FIGS.3 and 4. The fuel cell system 111 has an anode chamber 113 and a cathodechamber 114 which are separated by a proton conducting membrane 115, aswell as a temperature controlled circuit. The anode chamber 113, thecathode chamber 114 and the membrane 115 form a hydrogen fuel cell(PEMFC) in which electrical energy is produced by electrochemicalprocesses. This energy can be tapped at electrical conduit 112 aselectrical voltage and current.

The anode chamber 113 is connected to a blocking member, magnetic valve142, via an anode outlet 117. A separator 119 is located downstream ofthe blocking member 142 having a drain for water and an output for gasand feeds to the external environment via valve 148. The anode chamber113 is likewise connected to an anode circuit 116 which, via an anodeoutlet 117, a magnetic valve 124, and a fluid entrainment pump 125, isconnected to the anode inlet 123. In addition, the anode inlet 123 isconnected to a hydrogen tank 126 via at least one pressure reducer 147.The hydrogen tank could be a pressurized vessel or a metal-hydridestorage unit.

The cathode chamber 114 is connected to a blocking member, a magneticvalve 128, via a cathode outlet 127. A separator 140 is disposeddownstream of the blocking member 128 and has a drain for water and anoutlet for gases, which escape via valve 141 to the outside. The cathodeoutlet 127 is connected, between the cathode chamber and the magneticvalve 128, to the cathode inlet 130 via a cathode circuit 135 having amagnetic valve 129 and a fluid entrainment pump 139. In addition, thecathode chamber 114 is connected to an oxygen tank 133 via the cathodeinlet 130, a pressure reducer 131, and a magnetic valve 132. The cathodeinlet 130 is likewise connected to a compressor unit 137. One of theinputs of the unit 137 intakes air via a filter 138.

The fuel cell is likewise equipped with a temperature controlledcircuit. The cooling water is circulated via a circulation pump 122 pasta heater 120 and a cooler 118. A three-way thermostat valve 121facilitates bypass for the cooler 118 and for the heater 120 when thetemperature of the cell lies in the set-point region between 80 to 90°C. When the temperature falls below 70°, the thermostatic valve 121switches circulation through the switched-on heater powered by the powermains during the standby mode.

The anode chamber 113, the cathode chamber 114, the membrane 115, theanode circuit 116, the cathode circuit 135, the temperature controlledcircuit having the cooler 118, the heater 120 and the circulating pump122, separators 119 and 140, as well as the inlet and outlet conduitsthereof are accommodated within a housing 143. The housing 143 ispressure-tight, pressure resistant and heat insulated. The housing 143is connected to a tank 145 via an inlet 134 and a pressure reducer 144.The tank 145 contains nitrogen provided as a pressurizing agent.

When the alternating current power network 6 operates properly, the fuelcell system 111 is located in a standby state in which the magneticvalves 128 and 142 are closed. Magnetic valves 124 and 129 are alsoclosed and the magnetic valve 132 is opened. The closed magnetic valve128 and the opened magnetic valve 132 clause the cathode chamber 114 tobe filled with oxygen from the tank 133. The oxygen is present at apressure on the membrane 115. The pressure can be adjusted to a desiredvalue using a pressure reducer 131 e.g. 2 bar. However, since themagnetic valves 128 and 129 are closed, the oxygen cannot flow throughthe cathode chamber 114. The anode chamber 113 is filled with hydrogenfrom the tank 126, with the magnetic valve 142 being closed. Thehydrogen is present under pressure on the membrane 115. The pressure canbe adjusted to a desired value using pressure reducer 147 to, e.g. thesame pressure as that in the cathode chamber. Since the magnetic valves142 and 124 are closed, hydrogen cannot flow through the anode chamber.The nitrogen pressure present in the inner region 149 of the housing 143can likewise be adjusted via pressure reducer 144. The nitrogen can bereleased into the surroundings via a drain 146 and a burner (not shown).A pressurized (2 to 4 bar) fuel cell has leakage losses of approximately1 to 2 mbar per minute in the absence of a counter-pressure fromnitrogen in chamber 149. Accordingly, an explosive gas mixturecomprising H₂+O₂ would occur inside the housing after a certain periodof time. This is avoided by pressurizing the housing using N₂. Since asmall degree of H₂ diffusion cannot be completely avoided despite thisN₂ overpressure, a slow N₂ rinsing of the housing 143 is effected viathe drain 146 and the burner.

FIG. 4 shows a possible regulation of the gas pressure and flow. Thethree pressure reducers 131, 144 and 147 are adjusted to effect aconstant intermediate pressure step which e.g. reduces the pressure inthe containers of 200 bar to 6 bar. The fine adjustment is effected, ineach case, via three downstream PIC valves (pressure indicated control)150, 151, 152. When the network power is interrupted and H₂+O₂ usageoccurs, these valves remain open up to a predetermined value of thepressure. In the standby state, these valves are closed and the gasesare present at the predetermined pressure on the membrane 115. Each ofthe valves 150 and 151 in the H₂ and O₂ inlets has two FIC valvesupstream thereof (flow indicated control) 153, 154 for mass flowregulation.

The membrane 115 is proton conducting. The H₂ present in the anodechamber 113 emits electrons and hydrogen protons. The hydrogen protonspass through the membrane 115 and react with the oxygen in the cathodechamber 114 to produce water. The electrons produced by this chemicalreaction cause the above mentioned electrical voltage on the electricalcable 112.

The circulating pump 122, the heater 120 and the cooler unit 118 are inautomatically switched off and on in the standby state. Should thetemperature of the cell decrease in time and fall below a temperature ofe.g. approximately 70° C., the heater 120 is switched-on. The water iscirculated through the temperature control circuit and warmed.Components of the fuel cell system 111 which are switched-on in thestandby state are supplied with electrical energy from the alternatingcurrent power network 6.

Departing from the standby state, the manner of functioning of the fuelcell system in accordance with the invention in the event of a powerfailure will now be described with reference to the two embodiments 11and 111, respectively.

When the fuel cell system 11 or system 111, in the standby state, isinitially subjected to an electrical load, for example applied by theusers 2, the above mentioned voltage rapidly sinks due to the closed-offcathode chamber 14 or 114 and the associated limited amount of availableoxygen. The amount of current which can therefore be delivered by thefuel cell system at this point in time is therefore relatively small.The voltage and the current capacity depend on the volume of the anodechamber 13 or 113 and of the cathode chambers 14 and 114, that is tosay, on the number of available stacks.

However, in accordance with the invention, when a breakdown in thealternating power network 6 is detected by the control apparatus 9, themagnetic valves 28 and 128 are opened. The fuel cell system 11, 111 isthereby transferred into its operational state. The cathode chambers 14,114 are thereby no longer closed off and oxygen can flow through thecathode chamber 14, 114. Continuous chemical reactions can thereby takeplace in the fuel cell system 11, 111. The methanol/water mixturecontinuously reacts in the system 11 within the cathode chamber 13 withrelease of hydrogen protons and electrons to form carbon dioxide, thehydrogen protons pass through the membrane 15, 115 to react with theoxygen in the cathode chamber 14, 114 and produce water. Thecontinuously generated electrons produce a continuous current andvoltage, which is available for tapping by the cable 12, 112.

This electrical voltage on cable 12, 112 is buffered by the capacitor 10and passed onto the electrical users 12 via the DC-AC converter 7 andthe users are thereby provided with current from the fuel cell system11, 111. In this operational state the fuel cell system replaces thealternating current power network 6 energy supply to the user 2.

When the fuel cell system 11 has switched from the standby state intothe operational state, the bypass magnetic valves 35 and 42 are opened,in addition to the above mentioned magnetic valve 28. The motor 36 andthe compressor expander unit 37 as well as the pump 41 and the coolantpump 22 are also switched-on, and the heater 20 is switched-off.

Heat is produced by the continuous chemical reactions during theoperational state. The methanol/water mixture thereby leaves the anodechamber 13 with a temperature of approximately 110° and is then cooledby the cooler 18 to a temperature of about 40°. Gaseous carbon dioxideis separated in the downstream separator 19 and input to the catalyticburner 29 via the opened magnetic valve 42, where it is burned togetherwith likewise separated residual methanol. The exhaust gases whichthereby occur are expanded by the switched-on compressor-expander unit37 and water is recaptured with the assistance of the cooler 39. Thiswater can be introduced to the separator 19 in the anode circuit 16 viathe switched-on pump 41. The cooled methanol/water mixture present inthe separator 19 then regains entrance to the anode chamber 13 via thethermostat valve 21. The methanol/water mixture is thereby mixed via theseparator 24, in dependence on the thermostat valve 21, with exactlythat amount of hot methanol/water mixture which, together, produces amixture of approximately 90° to approximately 110°, which is thenpresent at the anode inlet 23. Excess hot methanol/water mixture ispassed out of the separator 24 into the cooler 18. In addition, thedosing pump 25 is switched on during the operational state of the fuelcell system 11 to introduce fresh methanol into the anode circuit 16.

In a first brief time period between approximately 2 seconds toapproximately 20 seconds, e.g. 4 to 5 seconds, following transition ofthe fuel cell system 11 from the standby state into the operationalstate, oxygen is introduced into the cathode chamber 14 from the tank33. During this period of time, the compressor-expander unit 37, whichis switched-on at the transition time, warms up to its operational rateof revolution. During this warm-up time, the air which is suctioned inby the compressing portion of the compressor-expander unit 37 via thefilter 38 is passed off via the opened bypass magnetic valve 35. Afterthe system has achieved its operational state, i.e. after expiration ofthe above mentioned time interval, the magnetic valve 34 is opened andthe bypass magnetic valve 35 is closed. The air intake of the pressureportion of the compressor-expander unit 37 is thereby introduced intothe cathode chamber 14. The cathode chamber 14 thereby acquires theoxygen necessary for the chemical reactions via this intake air. Themagnetic valve 32 is then closed so that no further oxygen can flow fromthe tank 33 into the cathode chamber 14.

In the fuel cell system 111, the magnetic valves 129, 142 and 124 arealso opened during the transition between the standby state into theoperational state, in addition to the magnetic valve 128. The magneticvalves 141 and 148 are initially closed in the operational state.

The gas feedback in the anode circuit 116 and the cathode circuit 117effects mixing between dry saturated exhaust gases and dry pressurizedoxygen and hydrogen. Additional moisturizing is not necessarilyrequired. The pressure loss associated with the re-circulation of thegases is compensated for with the assistance of entrainment pumps 125and 139.

In the operational state, the electrochemical reactions producesufficient heat so that the heater 120 is no longer needed. If excessivetemperatures are achieved, the circulating pumps can be utilized tobring the cooling water temperature to about 80° C. using the cooler118. The H₂O produced by the electrochemical reactions can then beseparated in the separators 119 and 140 and can be fed to thetemperature controlled circuit via a valve 156 or (the conduit is notshown) to an air moisturizer 155 in the conduit 130.

For power interruptions in excess of 18 s to 20 s, switch-over iseffected from oxygen operation to air operation. The compressor 137reaches its operational speed and intakes air via the filter 138. Afterthe air is pressurized, the magnetic valves 136 and 141 open and themagnetic valves 132 and cathode circuit magnetic valve 129 are closed.The valve 148 can be opened from time to time for gas removal reasons(purging). The air can also be moisturized via a humidifier 155. A massflow regulation of the H₂ flow, of the initial O₂ flow and of thesubsequent air flow is effected via the PIC and FIC valves 150, 151,152, 153, 154, which are opened during the operational state.

The electrical components of the fuel cell system 11 and 111 which areswitched-on during the operational state are thereby supplied withelectrical energy from the fuel cell system itself.

The fuel cell system thereby provides interruption-free power supply forthe user 2 during its operational state following breakdown of thealternating current power network 6 using the oxygen delivered from thetank 33, 133. After switch-over to the compressor 37, 137 and afterswitching-off tank 33, 133, the fuel cell system 11, 111 constitutes asubstitute network power system using substantially only methanol or H₂.The oxygen in tank 33, 133 and the nitrogen in tank 45, 145 are used toonly an insignificant extent, or not at all.

In the standby state, the amount of oxygen used, the amount of nitrogenused and the amount of H₂ or methanol used by the fuel cell system arealmost zero. Electrical energy is used only at certain times for theheater 20, 121 and the cooling pump 20, 120.

We claim:
 1. A fuel cell system comprising: an anode chamber; a cathodechamber; a proton conducting membrane disposed between and separatingsaid anode chamber and said cathode chamber; means for supplying fuel tosaid anode chamber during an operational state; means for supplying anoxidant to said cathode chamber during said operational state; means forfilling said anode chamber with fuel during a standby state; means forfilling said cathode chamber with oxidant during said standby state; andmeans for preventing oxidant flow through said cathode chamber duringsaid standby state, wherein said cathode chamber is connected to acathode outlet having a cathode outlet blocking member which is closedin the standby state.
 2. The fuel cell system of claim 1, wherein saidoxidant comprises gaseous oxygen and further comprising means for theexertion of pressure with said oxidant on said membrane.
 3. The fuelcell system of claim 2, wherein said oxidant comprises air and furthercomprising means for the exertion of pressure with said air on saidmembrane.
 4. The fuel cell system of claim 1, wherein said blockingmember comprises a magnetic valve.
 5. The fuel cell system of claim 1,wherein said cathode chamber is connected to a cathode inlet which, viaa first blocking member, is connected to a least one tank filled withsaid oxidant, wherein said first blocking member is opened during saidstandby state.
 6. The fuel cell system of claim 5, further comprising apressure reducer disposed in said cathode inlet.
 7. The fuel cell systemof claim 5, wherein said first blocking member comprises a firstmagnetic valve.
 8. The fuel cell system of claim 5, wherein the cathodechamber is connected, via said cathode inlet and a second blockingmember to a compressor means, said compressor means intaking gas.
 9. Thefuel cell system of claim 8, wherein said second blocking meanscomprises a second magnetic valve.
 10. The fuel cell system of claim 8,wherein said gas comprises air.
 11. The fuel cell system of claim 1,further comprising means for the exertion of pressure with said fuel onsaid membrane.
 12. The fuel cell system of claim 1, wherein said anodechamber is connected to an anode circuit.
 13. The fuel cell system ofclaim 12, wherein said fuel comprises a water/methanol mixture and saidanode circuit comprises temperature control means.
 14. The fuel cellsystem of claim 13, wherein said temperature control means comprise apump and a heater.
 15. The fuel cell system of claim 13, furthercomprising means for exerting pressure on said anode circuit with aninert gas.
 16. The fuel cell system of claim 15, wherein said inert gasconsists essentially of nitrogen.
 17. The fuel cell system of claim 1,wherein said fuel comprises hydrogen and aid anode chamber is connectedto an anode outlet having an anode outlet blocking member which isclosed in said standby state.
 18. The fuel cell system of claim 17,wherein said anode outlet blocking member comprises a third magneticvalve.
 19. The fuel cell system of claim 17, wherein said anode chamberhas an anode inlet connected to an anode circuit and said cathodechamber has a cathode inlet connected to a cathode circuit, said anodecircuit comprising a first fluid entrainment pump and a fourth blockingmember, said cathode circuit comprising a second fluid entrainment pumpand a fifth blocking member.
 20. The fuel cell system of claim 1,wherein said fuel cell system comprises a gas-tight housing, whereinsaid housing is connected to a gas pressure vessel.
 21. The fuel cellsystem of claim 20, wherein said housing comprises means for heatinsulation and wherein said pressure vessel contains nitrogen.
 22. Thefuel cell system of claim 1, further comprising a temperature controlcircuit.
 23. The fuel cell system of claim 1, further comprising meansfor interruption-free current supply to at least one electrical user,means for supplying energy to said user from an alternating currentpower network, and means for supplying energy from said fuel cell systemto said user in the event of breakdown in the alternating current powernetwork, wherein said fuel cell system is normally in the standby state.24. A method for operating the fuel cell system of claim 1, the methodcomprising the steps of: a) filling said anode chamber with fuel duringa standby state of the fuel system; b) filling said cathode chamber withoxidant, during said standby state, said anode chamber separated fromsaid cathode chamber by said proton conducting membrane; c) preventingoxidant flow through said cathode chamber during said standby state; d)detecting breakdown in an alternating current power network normallysupplying energy to a user; e) switching the fuel cell system into anoperational state following step d), wherein oxidant is permitted toflow through said cathode chamber; f) supplying fuel to said anodechamber following step e); and g) supplying oxidant to said cathodechamber following step e).
 25. The method of claim 24, furthercomprising preventing fuel flow through said anode chamber during saidstandby state.
 26. The method of claim 24, further comprising exertingpressure on said membrane with said fuel and said oxidant during saidstandby state.
 27. The method of claim 24, wherein step e) comprises thestep of opening a cathode outlet blocking member.
 28. The method ofclaim 27, wherein step b) comprises introducing oxidant into saidcathode chamber from a tank and step g) comprises suctioning a gas intosaid cathode chamber.
 29. The method of claim 28, wherein said gascomprises air.
 30. The method of claim 27, wherein step e) comprises thestep of opening an anode outlet blocking member.
 31. The method of claim24, further comprising keeping the fuel cell system under gas pressurewithin an inner chamber of a housing.
 32. The method of claim 31,wherein said gas pressure is exercised using nitrogen.
 33. The method ofclaim 24, further comprising maintaining the fuel cell at an operationaltemperature.